1. Field of Invention
The present invention relates generally to the construction industry, and, more particularly, to fasteners and associated methods to fastening reinforcement steel rebar rods.
2. Description of the Related Art
Concrete is an artificial, stone-like material used for various structural purposes, made by mixing cement and various aggregates, such as sand, pebbles, gravel, or shale, with water and allowing the mixture to harden. It is well known that concrete is strong in compression but relatively weak in tension. Reinforced concrete and reinforced masonry structures are extremely common, including in highway and roadway construction. Reinforced concrete is concrete containing iron or steel bars, strands, or mesh to absorb tensile and shearing stresses. Reinforcement steel rods, typically known as rebar rods, are usually formed from carbon steel and have ridges for better mechanical anchoring into the concrete. Steel and concrete have similar coefficients of thermal expansion so that temperature changes result in minimal stress for concrete structures reinforced with steel rods. Rebar rods come in different sizes, including in metric and standard United States units.
Typically, rebar rods are tied together and positioned in the structure's form prior to pouring the concrete. Rebar rods are commonly tied by hand. In the pigtail method, the worker uses precut wire and a twisting tool that looks like a pig's tail. In the pliers method, the worker uses a spool of wire and a pliers tool. These methods subject workers to physical risks and especially repetitive bending down to tie the rebar rods together. Workers can also connect rebar rods together using plastic spacers, rebar staples, and plastic cable ties, each of which has its drawbacks in addition to subjecting workers to physical risks and repetitive bending down. Plastic spacers, also called couplers, are generally expensive. Plastic spacers introduce another material into the reinforced concrete, and that material may not have the favorable thermal properties with respect to concrete that steel does. Rebar rods connected by plastic spacers may not be as strong as rebar rods connected by wire. Plastic spacers come in various sizes, and a given plastic spacer may be limited to a particular rebar rod size or range of sizes. Likewise, rebar staples come in various sizes, and a given rebar staple may be limited to a particular rebar rod size or range of sizes. If incorrectly sized, a too-large rebar staple can extend beyond the concrete. Like plastic spacers, plastic cable ties introduce another material and its associated thermal properties into the reinforced concrete.
In addition, automatic tying and fastening tools have been introduced into the market.